When You have systemd init daemon, You should use syntax as
linux ... systemd.unit=rescue.target
(see 'man systemd.target')
Or, SYSV4 init/upstart option are stil functioning, simply to linux kernel cmdline append 'single', 's', '1'
But You perhaps will find that systemd is almost unusable in rescue mode (in 'normal' multiuser/graphical mode it is only slightly better) when starting from installed system. It is better boot from CD/DVD/USB stick, Fedora or eg. System Rescue CD etc.